This invention relates to stabilization of micelles, and activation of micelles for delivery of substances such as drugs.
The efficacy of cancer chemotherapy is limited by toxic side effects of anticancer drugs. The ideal scenario would be to sequester the drug in a package that would have minimal interaction with healthy cells, then at the appropriate time, release the drug from the sequestering container at the tumor site. To achieve this goal, various long-circulating colloid drug delivery systems have been designed during the last three decades. A common structural motif of all these long circulating systems, whether they be nanoparticles, liposomes, or micelles, is the presence of poly(ethylene oxide) (PEO) at their surfaces. The dynamic PEO chains prevent particle opsonization and render them xe2x80x9cunrecognizablexe2x80x9d by reticulo-endothelial system (RES). [1] This invaluable advantage has promoted extensive research to develop new techniques to coat particles with PEO, techniques ranging from physical adsorption to chemical conjugation.
From the technological perspective, the most attractive drug carriers are polymeric micelles formed by hydrophobic-hydrophilic block copolymers, with the hydrophilic blocks including PEO chains. These micelles have a spherical, core-shell structure, with the hydrophobic block forming the core of the micelle, while the hydrophilic PEO block (or blocks) forms the shell. Block copolymer micelles have promising properties as drug carriers in terms of their size and architecture. The advantages of polymeric micellar drug delivery systems over other types of drug carriers include: 1) long circulation time in blood; 2) appropriate size (10 to 30 nm) to escape renal excretion but to allow for the extravasaation at the tumor site; 3) simplicity in drug incorporation, compared to covalent bonding of the drug to the polymeric carrier and 4) drug delivery independent of drug character. [2]
The ability of PEO-coated particles to prohibit adsorption of proteins and cells depends on the surface density of PEO chains, their length and dynamics. [1,3] However, only a few known block copolymers form micelles in aqueous solutions. Among them, AB-type block copolymers, e.g. poly(L-aminoacid)-block-poly(ethylene oxide) [2,3-13] and ABA-type triblock copolymers. Triblock copolymers of this class are available under the name PLURONIC(trademark), which shall be referred to generically herein as xe2x80x9cP-triblockxe2x80x9d. P-triblocks are block polymers of PEO and PPO, usually triblock PEO-PPO-PEO copolymers, where PPO stands for poly(propylene oxide); the hydrophobic central PPO blocks form micelle cores, whereas the flanking PEO blocks form the shell, or corona which protects micelles from the recognition by RES. P-triblock copolymers are commercially available from BASF Corp. and ICI. P-triblock polymers are also disclosed in U.S. Pat. No. 5,516,703 to Caldwell et al, issued May 14, 1996, which is hereby incorporated by reference. P-triblock structure in aqueous solution have been extensively investigated by many authors and have been recently reviewed by Alexandridis [22], see also [16]. The phase state of P-triblock micelles can be controlled by choosing members of the P-triblock family with appropriate molecular weight, PPO/PEO block length ratio, and concentration. The hydrodynamic radii of P-triblock micelles at physiological temperatures range between 10 and 20 nm, which makes them prospects as potential drug carriers.
Recently the synthesis of the poly(ethylene oxide-block-isoprene-block-ethylene oxide) triblock copolymer has been reported [23]. Isoprene blocks comprising the core of this copolymer were crosslinked by UV irradiation, rendering micelles stable in the circulation system of mice.
The incorporation of drugs into block copolymer micelles may be achieved through chemical and physical routes. Chemical routes involve covalent coupling of the drug to the hydrophobic block of the copolymer leading to micelle-forming, block copolymer-drug conjugates. However, this approach involved complex synthetic steps and purification procedures. This concept is disclosed in Rigsdorf, et al. [24] and Kataoka, et al. [7-10, 25-27]
Physical entrapment is a better way of loading drugs into micellar systems. Physical entrapment of the anti-cancer drug doxorubicin (DOX) in micelles composed of poly(ethylene oxide-block-b-benzyl L-aspartate) has been disclosed by Kataoka, et. al. [12].
Polymeric surfactants at various aggregation state have been tested as drug carriers. P-triblock molecules in the uniimeric form (below the critical micelle concentration, CMC) were found to sensitize multi-drug resistant (MDR) cancerous cells. Kabanov and Alakhov [20, 28, 29] have found that there is a-dramatic increase in Daunorubicin and DOX cytotoxic activity toward the multi-drug resistant cell lines while in the presence of 0.01 to 1% of PLURONIC P85 or L61. The efficacy of the drug/P-triblock systems dropped above the CMC. It was concluded that the efficacy of P-triblockdelivery systems was based on the presence of P-triblock unimers.
The drop in the efficacy of drug/P-triblock systems above the CMC may be due to the substantial decrease in the intracellular drug uptake from dense P-triblock micelles. [30-32] The drug incorporated into the micelle core is masked from the external media by the corona composed of PEO chains.
This phenomenon may be used advantageously to prevent the unwanted drug interactions with healthy cells. However, the challenge is to ensure drug uptake at the tumor site.
The fundamental difference between using polymeric surfactants below or above the CMC is that below the CMC the enhanced intracellular uptake and enhanced cytotoxicity of the drug delivered with P-triblock unimers is exploited [20, 28, 29, 33], whereas above the CMC, the shielding properties of P-triblock micelles are used to prevent unwanted drug interactions with healthy cells. To ensure drug uptake from (or together with) polymeric micelles at the tumor site, micelle perturbation and cell membrane permeabilization by ultrasound is being proposed [30-32, 34].
Summarizing, drug delivery using micellar drug carriers proved to have many advantages over the use of free drugs.
Some micellar systems are structurally stable (these are micelles with solid-like cores that dissociate slowly at levels below their CMC, e.g. micelles formed by poly(L-aminoacid)-block-poly(ethylene oxide) copolymers [2, 5, 26]). As indicated by NMR data, molecular motion in the core of these micelles is substantially frozen. In contrast, P-triblock micelles or those formed by poly(ethylene oxide-block-isoprene-block-ethylene oxide) triblock copolymer dissociate very fast upon dilution [16]. These micelles have xe2x80x9csoftxe2x80x9d cores, which means that at room temperature theft molecular segments are above corresponding glass transition temperature, Tg and move relatively fast. Since upon IV injections, the concentration of the polymeric drug carrier can drop to levels below the CMC, non-stable micelles require additional stabilization to be used in micellar form.
1. S. I. Jeon, J. H. Lee, J. D. Andrade, p. (3. D. Gennes, J. Colloid Interface Sci. 142-158,(1991) 149-158.
2. K. Kamoka, O. S. Kwon, M. Yokoyarna, T. Okano, Y. Sakurai, I. Control. Release 24, (1993) 119-132.
3. J.-T. Li, K. D. Caldwell, N. Rapoport, Langmuir 10, (1994) 4475-4482.
4. S. Cammas, K. Kataoka, in Solvents and Self-Organization of Polymers S. E. Webber, Ed. (Kluwer Academic Pubi., Netherland, 1996) pp. 83-113.
5. M. Yokoyama, in Advances in Polymeric Systems for Drug Delivery. T. Okano, Ed. (Gordon and Breach Science Publishers, Iverdon, Switzerland, 1994) pp. 24-66.
6. M. Yokoyarna, Polymeric micelles for drug delivery: their stratagy and perspectives., 17th International Symposium on Recent Advantages in Drug Delivery Systems. 1995), pp. 99-102.
7. M. Yokoyama, T. Okano, Y. Sakurai, H. Ekimoto, C. Shibazaki, K. Kataoka, Cancer Res. 51, (1991)3229-3236.
8. G. S. Kwon, M. Yokoyama, T. Okano, Y. Sakurai, K. Kataoka, Pharmac. Res. 10, (1993) 970-974.
9. G. Kwon, M. Naito, M. Yokoyama, Y. Sakurai, T. Okano, K. Kataoka, Langmuir 9, (1993) 1. S. I. Jeon, J. H. Lee, J. D. Andrade, p. (3. D. Gennes, J. Colloid Interface Sci. 142-158, (1991) 149-158.
10. G. S. Kwon, M. Yokoyama, T. Okano, Y. Sakurai, K. Kataoka, Enhanced tumor accumulation and prolonged circulation times of micelle-forming poly(ethylene oxide-co-aspartate) block copolymer-Adriamycin, conjugates., 6th International Symposium on Recent Advantages in Drug Delivery Systems 1993), pp. 175-176.
11. G. S. Kwon, K. Kataoka, Advanced Drug Delivery Reviews 16, (1995) 295-309.
12. G. S. Kwon, S. Suwa, M. Yokoyama, T. Okano, Y. Sakurai, K. Kataoka, Pharm. Res. 12, (1995) 192-195.
13. G. S. Kwon, M. Naito, K. Kataoka, M. Yokoyama, Y. Sakurai, T. Okano, Colloids and Surfaces B: Biointerfaces 2, (1994) 429-434.
14. A. V. Kabanov, E. V. Batrakova, N. S. Melik-Nubarov, N. A. Fedoseev, T. Y. Dorodnich, V. Y. Alakhov, I. R. Nazarova, V. A. Kabanov, I. Controlled Release 22, (1992) 141-158.
15. A. V. Kabanov, I. R. Nazarova, I. V. Astafieva, E. V. Batrakova, V. Y. Alakhov, A. A. Yaroslavov, V. A. Kabanov, Macromolecules 28, (1995) 2303-2314.
16. N. Rapoport, K. Caldwell, Colloids and Surfaces B: Biointerfaces 3, (1994) 217-228.
17. V. Yu. Alakhov, A. V. Kabanov, Expert Op Invest Drugs 7 (1998), 1453-1473.
18. E. V. Batrakova, T. Y. Dorodnych, E. Y. Klinskii, E. N. Kliushnenkova, O. B. Shemchukova, O. N. Goncharova, S. A. Aijakov, V. Y. Alakhov, A. V. Kabatiov, British Journal of Cancer 74, (1996) 1545-1552.
19. V. Y. Alakhov, E. V. Batrakova, T. Dorodnich, S. Li, A. Venne, A. V. Kabanov, Block copolymeric drug carriers: 1. delivery of antineoplastic drugs., First International Symposium on Polymer Therapeutics. (The School of Pharmacy, University of London, UK, London, 1996), pp. 213.
20. V. Alakhov, E. Moskaleva, E. Batrakova, A. Kabanov, Bioconjug. Chem. 7, (1996) 209-216.
21. N. Rapoport, in: 11th International Symposium On Surfactants In Solution. Jerusalem, Israel (1996), pp. 183.
22. P. Alexandridis, T. A. Hatton, Colloids and Surfaces A: Physicochemical and Engineering Aspects. 96, (1995) 1-46.
23. A. Rolland, J. O""Mullahe, P. Goddard, L. Brookman, K. Petrak, J. Appl. Polym. Sci. 44, (1992) 1195-1203.
24. K. Dorn, O. Hoerpel, H. Ringsdorf, in Bioactive Polymer Systems C. O. Gebelein, J. C. E. Canaher, Eds. (Plenum, New York, 1985) pp. 53 1-585.
25. M. Yokoyama, O. S. Kwon, M. Naito, T. Okano, Y. Sakurai, T. Seto, K. Kataoka, Bioconj. Chem. 3, (1992) 295-301
26. M. Yokoyama, Txcx9cSugiyama, T. Okano, Y. Sakurai, M. Naito, K. Kataoka, Pharmac. Res. 10, (1993) 895-899.
27. M. Yokoyama, G. S. Kwon, T. Okano, Y. Sakurai, H. Ekimoto, K. Kataoka, In vivo antitumor activity of polymeric micelle-anticancer drug conjugates against murine C 26 tumor., 6th International Symposium on Recent Advantages in Drug Delivery Systems. 1993), pp. 177-178.
28. V. Y. Alakhov, E. Y. Moskaleva, E. V. Batrakova, A. V. Kabanov, Bioconj. Chem. 7, (1996) 209-216.
29. A. Venne, S. Li, R. Mandeville, A. Kabanov, V. Alakhov, Cancer Research 56, (1996) 3626-3629
30. N. Rapoport, N. Munshi, L. Pitina, W. G. Pitt, Polymer Preprints 38, (1997) 620-621.
31. N. Rapoport J. N. Herron, W. G. Pitt, and L. Pitina, Micellar Delivery of Doxorubicin and its Paramagnetic Analog, Ruboxyl to HL-60 Cells: Effect of Micelle Structure and Ultrasound on the Intracellular Drug Uptake. J. Controlled Release, 1999, 58: 153-162.
32. N. Munshi, N. Rapoport, W. O. Pitt, Cancer Letters 117, (1997) 1-7.
33. D. Miller, E. Batrakova, T. Waitner, V. Alakhov, A. Kabanov, Bioconjug. Chem. 8, (1997) 649-657.
34. N. Rapoport, A. Smimov, A. Timoshin, A. M. Pratt, W. O. Pitt, Archives of Biochemistry and Biophysics 344, (1997) 114-124.
35. Ad. Smimov and R. L. Belford, Archives of Biochemistry and Biophysics 362, (1999) 233-241.
36. Z. Zhou, B. Chu, J. Colloid Interface Sci. 126, (1988) 171-180.
37. W. Brown, K. Schillen, M. Almgren, S. Hvidt, P. Bahadur, J. Phys. Chem. 95, (1991) 1850.
38. W. B. Pratt, R. W. Ruddon, W. D. Ensminger, J. Maybaum, Noncovalent DNA-Binding Drugs. The Anticancer Drugs (Oxford University Press, New York Oxford, 1994).
39. N. M. Emanuel, O. N. Bogdanov, V. S. Orlov, Russian Chemical Reviews 53, (1984)1121-1138.
40. N. M. Emanuel, N. P. Konovalova, L. S. Povarov, A. B. Shapiro, e. al., Russian Academy of Sciences, 1 3-(1-oxyl-2,2,6,6-tetramethylpiperylidenyl4)hydrozone rubomycin hydrochloride with a paramagnetic center and a method of producing same (1982).
41. M. D. Bednarski, J. W. Lee, M. R. Callstrom, K. C. Li, Radiology 204, (1997) 263-268.
42. Rediske A. M., Rapoport N, Pitt W. G., Reducing bacterial resistance to antibiotics with ultrasound, Letters in Applied Microbiology, 1999, 28: 81-84.
43. S. Stolnic, L. Illum, Davis, S. S., Long circulating microparticulate drug carriers. Advanced Drug delivery Reviews, 1995, 16:195-214.
44. Hoffman, A. S., Environmentally sensitive polymers and hydrogels: xe2x80x9csmartxe2x80x9d biomaterials. MRS Bulletin, 1991, 42-45
45. Kost, J., Langer, R., Responsive polymer systems for controlled delivery of therapeutics. Trends in Biotechnology, 1992, 10: 127-131
46. Lee, P. I., in controlled Release Technology: Pharmaceutical Application., Ed., P. I. Lee, W. R. Good. 1987, ACS, Washington, vol. 348, pp. 71-83.
47. Peppas, N. A., Hydrogels in Medicine and Pharmacy. Ed., AEds., N. A. Peppas, R. W. Korsmeyer, 1987, CRC Press, Boca Raton, vol. 3.
48. Siegel, R. A., in Pulsed and Self regulated Drug Delivery., Ed., AEds. J. Kost. 1990, Boca Raton, pp. 129-157.
49. Park, T. G., Hoffman, A S., Synthesis and characterization of pH- and/or temperature-sensitive hydrogels. J. Appl. Polymer Sci., 1992, 46:659-671
50. Kim, Y.-H., Kwon, I. C., Bae, Y. H., Kim, S W., Saccharide effect on the lower critical solution temperature of thermosensitive polymers. Macromolecules, 1995, 28:939-944
51. Kataoka, K., Koyo, H., Tsuruta, T., Novel pH-sensitive hydrogels of segmented poly(amine ureas) having a repetitive array of polar and apolar units in the main chain. Macromolecules, 1995, 28:3336-3341.
52. Jin, M. R., Wu, C F., Lin, P. Y., Hou, W., Swelling of and solute exclusion by poly(Nalkylacrylamide) gels. J. Appl. Polym. Sci., 1995, 56:285-288.
53. Chytry, V., Netopilik, M., Bohdanecky, M., Ulbrich, K., Phase transition parameters of potential thermosensitive drug release systems based on polymers of N-alkylmethacrylamides. L. Bionialer. Sci. Polymer Edn., 1997, 8:817-824.
54. Feil, H., Bae, Y. H., Feijen, J., and Kim, S. W., Effect of Comonomer Hydrophilicity and Ionization on the Lower Critical Solution Temperature of N-Isopropylacrylamide Copolymerand Macromolecules, 1993, 26:2496-2500.
55. Chen, M. -Q., Kishida, A., and Akashi, M., Graft Copolymers Having Hydrophobic Backbone and Hydrophilic Branches. XI. Preparation and Thermosensitive Properties of Polystyrene Microspheres Having Poly(N-isopropylacrylamide) Branches on Their Surfaces, Journal of Polymer Science: Part A: Polymer Chemistry, 1996, 34:2213-2220.
56. Idziak, I., Avoce, D., Lessard, D., Gravel, D., and Zhu, X. X., Thermosensitivity of Aqueous Solutions of Polyxcx9cN,N-diethylacrylamide). Macromolecules, 1999, 32: 1260-1263
57. Vernon, B., Gutowska, A., Kim, S W., and Bae, Y. H., Thermally Reversible Polymer Gels for Biohybrid Artificial Pancreas. Macromol. Symp., 1996, 109:155-167.
58. Vakkalanka, S K., Brazel, C S., Peppas, N. A., Temperature- and pH-sensitive terpolymers for modulated delivery of streptokinase. J. Bio mater. Sd. Polym. Ed., 1996, 8:119-129.
59. Stayton, P. S., Shimoboji, T., Long, C., Chilkoti, A., Chen, G., Harris, J. M., Hoffman, A. S., Control of protein-ligand recognition using a stimuli-responsive polymer. Nature, 1995, 378:472-474.
60. Jeong, B., Bae, Y. H., Lee, D. S., Kim, S. W., Biodegradable block copolymers as injectable drug-delivery systems. Nature, 1997, 388:860-862.
61. Chandehari, H., Kopeckova, P., Kopecek, J., In vitro degradation of pH-sensitive hydrogels containing aromatic azo bonds. Biomaterials, 1997, 18:861-872.
62. Chiu, H-C., Kopeckova, P., Deshmane, S. S., Kopecek, J., Lysosomal degradability of poly(a-amino acids). J. Biotned. Mater Res., 1997, 34:381-392.
63. Leroux, J. C., J. Biotned. Mater Res., 1994, 28:471-481.
64. Kataoka, K., Kwon, G. S., M. Yokoyama, Okano, T., Sakurai, Y., Block copolymer micelles as vehicles for drug delivery. J. Control. Release, 1993, 24: 119-132.
65. Yuan, F., Leuning, M., Huang, S. K., Berk, D. A., Papahadjopulos, D., Jam, R. K., Microvascular permeability and interstitial penetration of sterically-stabilized (stealth) liposomes in human tumor xenograft. Cancer Res., 1994, 54:3352-3356.
66. Kwon, G. S., Suwa, S., Yokoyama, M., Okano, T., Sakurai, Y., Kataoka, K., Enhanced tumor accumulation and prolonged circulation times of micelle-forming poly(ethylene oxideaspartate) block copolymers-adriamicin conjugates. .1. Contr Release, 1994, 29:17-23.
67. A. V. Kabanov and V. Yu. Alakhov, Micelles of amphiphilic block copolymers as vehicles for drug delivery in: Amphiphilic Block Copolymers: Self Assembly and Applications, Ed. P. Alexandridis and B. Lindman. Elsevier, Netherland, 1997
68. N. Y. Rapoport, Stabilization and Acoustic Activation of Pluronic Micelles for Tumor-Targeted Drug delivery. Colloids and Surfaces B: Biointerfaces 16 (1999) 93-111
69. Tian, M., Qin, A., Ramireddy, C., Webber, S., Munk, P., Hybridization of block copolymermicelles. Langmuir, 1993, 9:1741-1748
70. Emanuel, N. M., Konovalova, N. P., Dyachkovskaya, R. F., Potential anti-cancer agents-nitroxyl derivatives of Rubomicin. Neoplasma, 1985, 32: 285-292.
71. Konovalova, N. P., Dyachkovskaya, R E., Ganieva, L. K., Volkova, L. M., lapshin, I. M., Rudakov, B. Y., Shaposhnikov, Y. G., Shapiro, A. B., Subrenal capsule assay of human tumor chemosensitivity. 1991,38:275-284.
72. Rapoport, N., Pitina, L., Intracellular distribution and intracellular dynamics of a spin-labeled analog of doxorubicin by fluorescence and EPR spectroscopy. J. Pharm. Sci., 1997, 87:321-325.
73. Domb, A. J., Langer, R., Polyanhydrides: 1: Preparation of high molecular weight polymers. J. Polym. Sci., A, Polym. Chem., 1987, 25:3373-3386.
74. Domb, A. J., Nudelman, R., in vivo and in vitro elimination of aliphatic polyanhydrides. Biomateriabs, 1995, 16:319-323
75. Barrett, A. J., Heath, M. F., in Lysosomes: A laboratory handbook, Ed. J. T. Dingle. 1977, Elsevier, Amsterdam, pp. 19-145.
76. G. S. Kwon and K. Kataoka, Block Copolymer Micelles as long circulating drug-vehicles. Advanced Drug Delivery Reviews 16 (1995) 295-309.
77. G. S. Kwon, M. Naito, M. Yokoyama, T. Okano, Y. Sakurai, and K. Kataoka, Block copolymer micelles for drug delivery: loading and release of doxorubicin. J. Control. Release 48 (1997) 195-201.
78. M. E. Johnson et al. J. Pharm Sci. 85 (1996) 670-677.
79. K. Tachibana, T. Uchida, K. Ogawa, N. Yamashita, and K. Tamura, Induction of cell-membrane porosity by ultrasound. Lancet 353 (1999) 1409.
80. J. Liu, T. N. Lewis, and M. R. Prausnitz, Non-invasive assessment and control of ultrasound mediated membrane permeabilization. Pharm. Res. 15 (1998) 918-924.
81. C. L. Christman, A. J. Carmichael, M. M. Mossaba, and P. Riesz, Evidence for free radical produced in aqueous solutions by diagnostic ultrasound. Ultrasonics 25 (1987) 31-34.
82. N. Y. Rapoport, A. I. Smimov, Interactions of spin-labeled anthracyclin with DNA, proteins and lipid bilayers: an electron paramagnetic resonance study, submitted to Archives Biochem. Biophys., 2000.
83. S. Mitragotri, D. Blankschtein, and R. Langers, Transdermal drug delivery using low-frequency sonophoresis. Pharm. Res. 13 (1996) 411-420.
84. P. Alexandridis, J. F. Holzwarth, and T. A. Hattons, Micellization of Poly(ethylene oxide)-Poly(propylene oxide)-Poly(ethylene oxide) Triblock Copolymer in Aqueous Solutions: Thermodynamics of Copolymer Association. Macromolecules 27 (1994) 2414
It is, therefore, an object of the invention to provide a system for the stabilization of micelles.
Another object of the invention is to provide a system for activation of stabilized micelles.
It is further an object of the invention to provide a system for drug delivery by the stabilization and activation of micelles.
Further objects of the invention will become evident in the description below.
The present invention involves various routes of micelle stabilization against degradation upon dilution. The invention also involves the effect of ultrasound on drug release from micelles and drug uptake by cancerous cells. In practice of the present invention, a drug can be encapsulated in a long-circulating micelle. Extravasation proceed only at tumor sites due higher permeability of blood vessels, and is enhanced by ultrasound. The micelle-encapsulated drug is accumulated at the tumor site. The uptake of the micelle-encapsulated drug is enhanced by ultrasound.
The advantages of the micelle drug carriers of the invention included long circulation time in the blood, appropriate size to escape renal excretion, appropriate size to allow for extravasation at the tumor site, and simplicity of drug loading. In addition, sterilization is possible by filtration, and micelles can be introduced by intravenous injections.
The micelles are formed from any suitable micelle forming block copolymer, including AB-type, and ABA-type. Exemplary micelle forming block polymers are the, polymers of the P-triblock family.
To be used as drug carriers, P-triblock micelles require stabilization to prevent degradation caused by significant dilution accompanying IV injection. Three routes of P-triblock micelle stabilization are included in the present invention The first route is direct radical crosslinking of micelles cores which results in micelle stabilization.
In the second method, a small concentration of an oil, such vegetable oil (about 0.0005 percent)is introduced into diluted P-triblock solutions. This substantially decreases micelle degradation upon dilution while not compromising drug loading capacity of oil-stabilized micelles. The amount oil used is much small than that required to form an emulsion, which is about 1 percent. The oil bonds or interacts with the core to make it more hydrophobic and stable, but it is insufficient to form an emulsion of the oil in water.
The third route is a technique based on polymerization of the temperature-responsive LCST hydrogel in the core of P-triblock micelles. The hydrogel phase is in a swollen state at room temperature, which provided for a high drug loading capacity of the system. The hydrogel collapses at physiological temperatures which locked the core of micelles thus preventing them from fast degradation upon dilution. This new drug delivery system is referred to herein as xe2x80x9cP-gelxe2x80x9d. Phase transitions in P-gel caused by variations in temperature or concentration were studied by the EPR.
The effect of P-triblock concentration in the incubation medium on the intracellular uptake of two anti-cancer drugs was studied. At low P-triblock concentrations, when the drugs were located in the hydrophobic environment, drug uptake was increased, presumably due to the effect of a polymeric surfactant on the permeability of cell membranes. In contrast, when the drugs were encapsulated in the hydrophobic cores of P-triblock micelles, drug uptake by the cells was substantially decreased. This may be used advantageously to prevent undesired drug interactions with normal cells. Ultrasonication enhanced intracellular drug uptake from dense P-triblock micelles. These findings permitted the formulation of a new concept of a localized drug delivery.
An advantage is that the p-gel micelles are stable for drug delivery, but not so stable that they cannot be degraded by the body. After a matter of weeks, the stabilized p-gels will gradually destabilize. This allows sufficient time to function effectively as a drug delivery system, but the degradation will allow eventual removal from the body. This is unlike many drug delivery systems that involve stable components that are slow to be removed from the body. The thermodynamics of the p-gel system direct the system toward dissolution, and instability, but the kinetics are very slow.
Another aspect of this embodiment is the use of hydrogels that are stimuli responsive to other environmental states, such as pH.
Other substances that are introduced into the body, other than drugs, can be encapsulated and delivered by the stabilized micelle system of the invention.
Another aspect of the invention is the use of pulsed ultrasound to release an encapsulated drug. In particular, for hydrogel stabilized micelles, the release of drug by ultrasound is reversible, with allows a highly controlled release of drug using a pulsed ultrasound system.